All electromagnetic waves, including visible light, radio waves, microwaves, X-rays, and gamma rays, propagate through a vacuum at the same speed, known as the speed of light in a vacuum. This speed is approximately 299,792,458 meters per second (or about 186,282 miles per second) and is denoted by the symbol "c."
According to the theory of special relativity, this speed, denoted as the universal constant "c," is a fundamental property of the fabric of spacetime. It represents the maximum speed at which information or energy can travel through the universe.
Regardless of the wavelength, frequency, or energy of an electromagnetic wave, all electromagnetic radiation travels through a vacuum at this constant speed. This fundamental property of electromagnetic waves in a vacuum is one of the key principles in physics and has been experimentally confirmed through numerous observations and measurements.